In last year's report we reported that peripheral blood lymphocytes from patients with winter depression had different in vitro responses to mitogen following bright light treatment compared to placebo treatment. This year the same study was repeated with a different group of patients and the observations were the same as that noted in the first study. To gain some further understanding of the mechanism by which light affected the cellular immune response, a group of normal volunteers was exposed to bright light or ordinary light restricted to their eyes. The data from this study were quite clear, showing that light perceived through the eyes is transduced through the central nervous system, impacting on the cellular immune response.